Hardenable sheet materials

ABSTRACT

A water-hardenable sheet material comprising a flexible web having deposited thereon an intimate mixture of a water soluble poly(carboxylic acid) or a precursor thereof and an ion leachable inorganic particulate material.

This is a continuation, of Ser. No. 525,731 filed Nov. 21, 1974 nowabandoned.

This invention relates to hardenable sheet materials and moreparticularly to sheet materials which harden on contact with water.Water-hardenable sheet materials have a variety of applications, forexample, in orthopaedic surgery they are widely used as splintingmaterials. Traditionally, bandages comprising plaster-of-Paris aresoaked in water and then applied to the affected limb. Theplaster-of-Paris hardens within a few minutes to form a rigid casing.Although plaster-of-Paris casts are adequate for some applications, theyare heavy, not wholly resistant to water, and partially opaque tox-rays. In addition, plaster-of-Paris casts usually take at least twentyfour hours to develop their maximum strength, and this time may beconsiderably longer in high humidity environments. If a plaster-of-Pariscast is stressed whilst in the "green" state, that is to say before ithas reached its maximum strength, it is liable to delaminate, leading toincipient failure of the cast. In some applications these disadvantagescan be quite serious, and for this reason many attempts to find analternative to plaster-of-Paris have been tried. For example, it hasbeen suggested to use a polymerisable resin system which is polymerisedby ultraviolet light. However, this requires the use of specialisedtechniques, and of course involves the expense of a suitable ultravioletlight source. For many surgical applications there is a need for asplinting material which is simple to use, hardens at room temperaturewithout the evolution of substantial amounts of heat, has a high greenstrength, develops its maximum strength as rapidly as possible, isnon-toxic, resistant to hot and cold water, and transparent to x-rays.

In recent years, a range of dental cements have been developed known asthe poly(carboxylate) cements and these are described and claimed inBritish Pat. Nos. 1,139,430 and 1,316,129. These materials normallycomprise an ion-leachable powder and an aqueous solution of apoly(carboxylic acid) which when mixed together form a cement of greatmechanical strength and water resistance.

The present invention provides a water-hardenable sheet material inwhich the hardening reaction involves the formation of apoly(carboxylate) cement.

According to the present invention, a water-hardenable sheet materialcomprises a flexible web having deposited thereon an intimate mixture ofa water soluble poly(carboxylic acid) or a precursor thereof and anion-leachable inorganic particulate material.

The term "sheet" is used in the sense of a body whose breadth is largein comparison with its thickness. The flexible web may be woven, laiddown as a non-woven fabric, cast, or extruded. It is preferred that theweb be permeable in order to aid the deposition thereon of the watersoluble poly(carboxylic acid) or precursor thereof and the ion-leachableinorganic particulate material. For surgical applications, a permeableweb has the further advantage that it can allow access of air to theencased limb. The web most preferably has a porous structure, and in thecase of woven or non-woven fabrics, the porosity of the web may beconditioned by the method of manufacture, so that this particularcharacteristic may be predetermined to suit any special requirements.

The flexible web may comprise an organic natural or synthetic polymericmaterial, and particularly a cellulosic fibrous material such as cottonor other vegetable fibres, animal fibres such as wool, and syntheticpolymeric fibrous material such as polyamides, polyesters, and celluloseacetates. The flexible web desirably has sufficient mechanical strengthto enable it to act as a reinforcement for the sheet material. Forsurgical applications very good results have been obtained using acotton bandage fabric, for example of leno weave. The cotton fibres maybe reinforced with glass fibre if desired. Although less preferred, theflexible web may also be in the form of an impermeable film or foil ofplastic or other suitable material.

The preferred poly(carboxylate acids) are those prepared by thehomopolymerisation and copolymerisation of unsaturated aliphaticcarboxylic acids for example acrylic acid, itaconic acid, mesaconicacid, citraconic acid, and aconitic acid, and copolymerisation of theseacids with other unsaturated aliphatic monomers, for example, acrylamideand acrylonitrile. Particularly preferred are the homopolymers ofacrylic acid, and its copolymers, particularly with itaconic acid.

The preferred copolymers are those prepared by the copolymerisation ofacrylic acid with other unsaturated aliphatic carboxylic acid, forexample 2-chloro acrylic acid, 3-chloro acrylic acid, 2-bromo acrylicacid, 3-bromo acrylic acid, methacrylic acid, itaconic acid, maleicacid, glutaconic acid, aconitic acid, citraconic acid, mesaconic acid,fumaric acid, and tiglic acid. Other suitable monomers forcopolymerising with acrylic acid include unsaturated aliphatic compoundssuch as for example acrylamide, acrylonitrile, vinyl chloride, allylchloride, vinyl acetate, and 2-hydroxy ethyl methacrylate. Ter- andhigher polymers may be used if desired. Particularly preferred are thecopolymers of acrylic acid and itaconic acid. Preferably the mole ratioof acrylic acid to unsaturated aliphatic compound is from 19:1 to 2:1.

The acrylic acid copolymer solution may be prepared by polymerising theappropriate monomers in aqueous solution in the presence of a freeradical initiator, for example, ammonium persulphate and various chaintransfer agents, for example, isopropyl alcohol to give a solutioncontaining up to about 30% by weight of the copolymer. Such a solutionmay then be concentrated, if necessary. The copolymer solutions of thisinvention are preferably prepared by polymerising the monomers inboiling water, that is to say at temperatures at or around 100° C., andparticularly at temperatures of from 90° to 100° C. These temperaturesare considerably higher than those customarily used in conventionalaqueous polymerisation techniques.

Good results have also been obtained using a copolymer of vinyl methylether and maleic acid. Any suitable route may be used for thepreparation of the poly(carboxylic acid) and for example, polyacrylicacid may be prepared by hydrolysis of polyacrylonitrile. It is alsopossible to use a precursor of a poly(carboxylic acid) which will betransformed into the poly(carboxylic acid) on contact with water, forexample, a poly(carboxylic acid anhydride) or other suitable polymer.The poly(carboxylic acid anhydride) may be a homopolymer of anunsaturated carboxylic acid anhydride, or a copolymer with a vinylmonomer, and particularly a vinyl hydrocarbon monomer. Particularly goodresults may be obtained using homopolymers of maleic anhydride, andcopolymers thereof with ethylene, propene, butene and styrene.

The poly(carboxylic acid) or percursor thereof is preferably linear,although branched polymers may also be used, and preferably has anaverage molecular weight of from 1,000 to 1,000,000 and most preferablyfrom 10,000 to 100,000. In this specification the average molecularweight is defined as being that measured by gel permeationchromatography.

The poly(carboxylic acid) is preferably in fine particulate form, andmost preferably with a degree of fineness such that it will pass througha 150 BS mesh sieve.

The ion-leachable inorganic particulate material may for examplecomprise a di- or polyvalent metal oxide, preferably one that has beendeactivated, for example by heat treatment as described in British Pat.No. 1139430, or by partially coating the surface of the metal oxideparticles with an organic acid such as stearic acid. A preferred metaloxide is zinc oxide, to which there may be added up to about 10% byweight of other metal oxides such as, for example magnesium oxide. Thedi- or polyvalent metal oxide may if desired be replaced by a salt ofthe di- or polyvalent metal with a weak acid, the weak acid beingcapable of an exchange reaction with the poly(carboxylic acid) used, forexample zinc oxide may be wholly or partially replaced by zinc borate.Alternatively, the ion-leachable inorganic particulate material maycomprise a fused oxide made by heating a mixture of simple oxides tofusion temperature or an oxide glass, for example a glass comprisingcalcium or sodium oxide with alumina and silica. The preferredion-leachable inorganic materials for use in the present invention arealuminosilicate glasses, wherein the ratio by weight of acidic to basicoxides in the glass is such that the glass will react with apoly(carboxylate acid) in the presence of water to produce apoly(carboxylate) cement. It has been found that the rate of reactionincreases with increasing basicity of the aluminosilicate glass and thusthe ratio of the oxides in the glass composition can be chosen in orderto allow adequate working time to form the water-hardenable sheetmaterial into a desired shape before it has set. For many applicationsit is preferable to attain a working time of about 5 minutes, or less,and then to have the shortest possible setting time in which the sheetmaterial hardens and attains an appreciable rigidity and mechanicalstrength. Suitable aluminosilicate glasses may, for example, be preparedby fusing mixtures of alumina, silica, and calcium oxide in theappropriate proportions, together with, if necessary, up to 30% byweight, based on the total weight of the composition, of a flux whichmay be a fluoride, a borate, a phosphate, or a carbonate.

In this specification the glass compositions are described in theconventional manner as containing alumina, silica, calcium oxide, sodiumoxide and other oxides though it is to be understood that these oxidesare chemically combined in the matrix of the aluminosilicate glass, andare not present as free oxides. The proportions of oxides quoted for theglass compositions refer to the amounts of these oxides (added in somecases as the corresponding carbonates) added to the glass frit.

The weight ratio of the acidic oxides to basic oxides in thealuminosilicate glass is usually chosen such that the poly(carboxylate)cement stiffens within a relatively short period, termed the workingtime, which is usually less than ten minutes. It has been found that therate of reaction increased with increasing basicity of the glass andthus the ratio of the oxides can be chosen in order to allow adequateworking time to form the cement into a desired shape before it is hasset. For many applications it is preferred to attain a working time ofabout five minutes, or less, and then to have the shortest possiblesetting time in which the set cement hardens and attains an appreciablecompressive strength. Preferably the ratio by weight of acidic to basicoxides in the glass is from 0.1 to 3.0 and most preferably from 0.2 to2.5.

The principal acidic oxide in the aluminosilicate glass is silica,although the glass may also contain minor amounts of phosphoruspentoxide, and boric oxide. The principal basic oxide in the glass isalumina, which, although it has amphoteric properties, can be consideredfor the purposes of the present specification solely as a basic oxide.Particularly preferred aluminosilicate glasses fall within thecomposition range of 10 to 65% w/w silica, and 15 to 50% w/w alumina.

The aluminosilicate glass desirably contains at least one other basicoxide, preferably calcium oxide, which may be present in the glasscomposition in an amount of from 0 to 50% w/w. The calcium oxide may bepartly or wholly replaced by sodium oxide or another basic oxide ormixture of basic oxides, although in some applications the presence ofsodium oxide may be undesirable as this oxide tends to increase thesolubility of the resultant cement.

Preferred glasses for use in the present invention containing alumina,silica and calcium oxide are the gehlenite and anorthite glasses, and ingeneral glasses falling within the composition range to 10 to 65% w/wsilica, 15 to 50% w/w alumina and 0 to 50% w/w calcium oxide. Certain ofthe glasses within this general range, more particularly those having aweight ratio of calcium oxide to silica greater than 0.92 or having aweight ratio of calcium oxide to alumina less than 0.74 are newmaterials and are accordingly included within the invention.

The aluminosilicate glasses of the present invention may be prepared byfusing mixtures of the components in the appropriate proportions attemperatures above 900° C. and preferably in the range of 1050° C. to1550° C. The mixture is preferably fused for from 1 to 4 hours. Silicaand alumina may be included in the mixture as oxides, but it isconvenient to add calcium oxide and sodium oxide as calcium carbonateand sodium carbonate respectively, and references to the presence ofthese oxides in the glass fusion mixture includes the possibility thatthey may be added as carbonates or as other compounds which decomposesimilarly under glass fusion conditions to give the oxides.

The addition of carbonates to the fusion mixture lowers the fusiontemperature and thus these can be considered as fluxing agents. Ifdesired, however, the mixture may contain an additional fluxing agent,and this has been found to be important with glass compositionscontaining less than 10% w/w of calcium oxide. In this connectionfluorides such as fluorite and cryolite have been found to be especiallyuseful as fluxing agents, although as previously mentioned it isdesirable not to use large amounts of fluorides in the fusion mixture.Accordingly the amount of fluorine in the composition is preferably lessthan 14% by weight, most preferably less than 8% by weight, based on thetotal weight of the composition. It has been found that very goodresults may be obtained using fluorite (CaF₂) as a fluxing agent in anamount such that the fluorite is less than 15%, or greater than 90%, ona molar basis, of the total amount of fluorite and calcium oxide presentin the glass composition. Other fluxing agents, for example calciumphosphate and aluminium phosphate may also be used, though these areless preferred. The total amount of fluxing agents present in themixture, including carbonates, may be up to 50% by weight, based on thetotal weight of the mixture.

After fusion the glass may be poured off and cooled rapidly, forexample, in air or water or some combination of both. To a firstapproximation the proportions of the different elements in the glass maybe taken as the proportions of the same elements present in the mixture.Some fluorine may, however, be lost from a fluoride fluxing agent duringthe reaction.

The glasses used in the present invention may be readily obtained infine powder form. The degree of fineness of the powder should preferablybe such that it produces a smooth cement paste which sets within anacceptable period when mixed with the poly(carboxylic acid) in thepresence of water. Preferably the degree of fineness of the powder issuch that it will pass through a 150 mesh B.S. sieve and most preferablysuch that it will pass through a 350 mesh B.S. sieve. Mixtures ofdifferent glasses may be used if desired. Most preferably, however, theion-leachable inorganic particulate material comprises afluoroaluminosilicate glass, for example as described and claimed inBritish Pat. No. 1,316,129, wherein the ratio by weight of silica toalumina is from 1.5 to 2.0 and the ratio by weight of fluorine toalumina is from 0.6 to 2.5 or wherein the ratio by weight of silica toalumina is from 0.5 to 1.5 and the ratio by weight of fluorine toalumina is from 0.25 to 2.0. The fluoroaluminosilicate glasses may beprepared by fusing mixtures of silica, alumina, cryolite, and fluoritein the appropriate proportions at a temperature above 950° C. Suitablemethods for preparing the glasses are described in the aforementionedBritish Patent.

The degree of fineness of the ion-leachable inorganic particulatematerial should preferably be such that when the water-hardenable sheetmaterial is contacted with water it sets in the desired shape within anacceptable period. Preferably the degree of fineness of theion-leachable inorganic particulate material is such that it will passthrough a 150 mesh B.S. sieve and most preferably such that it will passthrough a 350 mesh B.S. sieve. Where the ion-leachable inorganicmaterial comprises an aluminosilicate glass, this may be used in theform of glass fibres if desired.

In a preferred method of preparing the water-hardenable sheet materialsof this invention, the ion-leachable inorganic particulate material isslurried in a dispersion or solution of the poly(carboxylic acid) orprecursor thereof in a suitable organic solvent, for example methylethyl ketone, cyclohexanone or methylene dichloride. The flexible web isthen impregnated with the slurry by a coating technique, and the organicsolvent removed, for example by evaporation. The amount of slurrydeposited on the flexible web may be varied within wide limits, butpreferably the deposited ion-leachable inorganic particulate materialand poly(carboxylic acid) or precursor thereof comprise from about 5 toabout 95% by weight, preferably from 60 to 90% by weight, of the totalweight of the water-hardenable sheet material. The acid and theion-leachable inorganic particulate material are preferably present inthe ratio of 1 to 100 parts by weight of ion-leachable inorganicparticulate material for each 10 parts by weight of the poly(carboxylicacid) or precursor thereof.

Preferably, the slurry comprises a binder to assist the adherence of theion-leachable inorganic particulate material to the flexible web.Suitable binders include polyvinyl alcohol, polyvinyl acetate andpartially hydrolysed polyvinylacetate. Usually only small quantities ofthe binder are required, for example up to about 5% by weight based onthe combined weight of the acid and the inorganic material, andpreferably from 0.1 to 1%.

The water-hardenable sheet material may comprise additional components,for example chemically unreactive particulate fillers may be included toeffectively eliminate any slight contraction which may take place onhardening of the hardenable sheet material. The particulate inert fillermay be selected from a wide range of suitable inorganic and organicmaterials, but it is preferred to use materials having good packingproperties and high compressive strength such as for example sand, talc,and fibrous materials such as asbestos and nylon fibres. Ion leachablecement powders for poly(carboxylate) cements are usually ground to size,thus producing a collection of irregular particles having poor packingproperties. Although the invention is not limited to any particulartheory, it is believed that the most suitable fillers are those ofregular shape which help to minimise the poor packing properties of thecement powder. Preferably the particle size of the inert filler is lessthan 100 B.S. mesh, and most preferably from 100 to 300 B.S. mesh suchas for example about 150 mesh. Very good results have been obtainedusing graded sand of particle size 100 to 200 B.S. mesh. The inertfiller should be substantially unreactive under the reaction conditions,but is preferably a material to which the poly(carboxylate) cement willadhere. The particulate inert filler may be separate from or included inany of the components of the cement pack and is preferably present in anamount of from 10 to 65% by weight, and most preferably from 25 to 50%by weight, based on the total weight of the components.

It is also often found advantageous to add a water soluble chelatingagent such as tartaric acid to the water-hardenable sheet material asthis has been found to decrease the setting time of poly(carboxylate)cements and increase the strength of the set cement. The chelating agentis added to the poly(carboxylic acid) in an amount sufficient to obtainthe desired working time and hardening rate. It is usually not necessaryto add more than about 20% by weight of the chelating agent based uponthe weight of the poly(carboxylic acid) and preferably the chelatingagent is present in an amount of from 0.01 to 10% by weight, such as forexample about 5% by weight, based on the weight of the poly(carboxylicacid). A wide range of chelating agents may be used in the presentinvention, particularly those containing chelating hydroxy or carboxylgroups or both, such as for example, ethylene diamine tetraacetic acid,salicylic acid, citric acid, 2,4 and 2,6-dihydroxybenzoic acids,dihydroxy tartaric acid, nitrilotriacetic acid, tartaric acid, melliticacids and polyglycols. Excellent results have been obtained using 5% byweight of tartaric or citric acid. Alternatively, the chelating agentmay be added in the form of a metal chelate, particularly a di- ortri-valent metal chelate. Examples of especially suitable metal chelatesinclude complexes of β-diketones with aluminium and chromium, forexample aluminium and chromium triacetylacetonates, and ethylene diaminetetraacetic acid complexes of zinc and copper.

In low humidity environments, poly(carboxylate) cements tend to losewater and this may have a slight detrimental effect upon the strength ofthe hardened sheet material. This effect may be substantially overcomeby including in the slurry to be applied to the flexible web a waterinsoluble polymer. Such a polymer may, for example, be dissolved oremulsified in the organic solvent so that after removal of the solventthe water insoluble polymer is in particulate form, intimately mixedwith the other components. The water insoluble polymer preferablycomprises pendant carboxylic acid groups which can take part in thehardening reaction, and for example it may comprise a copolymer of anunsaturated aliphatic carboxylic acid for example acrylic acid,methacrylic acid and itaconic acid, and an unsaturated aliphatic ester,for example an acrylic ester such as methyl methacrylate, ethyl acrylateand ethyl methacrylate. Good results may be obtained using a copolymerof methacrylic acid and ethyl acrylate. Alternatively the waterinsoluble polymer may be applied to the water-hardenable sheet materialas an aqueous emulsion at the time of use.

When used as splinting materials, the water-hardenable sheet materialsof this invention are designed to be used by the practitioner in thesame manner as the conventional plaster-of-Paris splinting materials.Thus the water-hardenable sheet material in the form of a roll may becontacted with water by, for example, dipping or spraying, and thenwound around the limb which it is desired to encase, overlappingadjacent turns as required. The sheet material is initially flexibleenabling it to be formed into a desired shape prior to hardening. Withina relatively short time, usually a few minutes, however, the hardeninghas proceeded to an extent sufficient to produce a hard tough cast. Thehardening reaction may be accelerated by the use of warm water.

The water-hardenable sheet materials of the present invention may alsofind applications outside conventional surgical use, for example theymay be used in forestry to repair damaged branches of young trees, andmay find application as modelling materials for children.

The invention is illustrated by the following Examples:

EXAMPLE 1

This Example describes the production of a water-hardenable sheetmaterial according to the present invention and its application to themanufacture of surgical splints.

80.0 gms. of a fluroaluminosilicate glass powder prepared as describedin Example 2 of British Pat. No. 1,316,129 and having a particle size of350 B.S. mesh are intimately mixed with 24.4 gms. of finely powderedpolyacrylic acid of average molecular weight 90000 and water content 8%by weight. This mixture is slurried in methylethyl ketone to give asuspension of about 40% solids, and 0.5 gm. of poly(vinyl acetate)binder added. With the suspension in agitation, 50 mm width leno gauzebandage is passed through and the pick-up of solids controlled with adoctor blade. The methylethylketone is removed by drying under a hot airblower whereupon the gauze can be rolled up in the manner of aconventional bandage.

The coated gauze is then sprayed with water, and wound around acylindrical mandrel, smoothing the turns by hand. The turns of the gauzeare allowed to overlap so that on hardening, after 30 minutes, the gauzecan be removed from the mandrel as a hollow cylindrical cast. After 48hours the cast is cut up into rings, mounted in an Instron machine andsubjected to compression at a rate of 5 mm.min⁻¹. The stresses forstrains of 5%, 10% and 12.5% are calculated. For the purposes ofcomparison, a plaster-of-Paris cast is prepared in the same manner andsimilarly tested for compressive strength. The results are given below:

                  TABLE 1:                                                        ______________________________________                                                                       Plaster-                                       Specimen Ring Dimensions                                                                        Poly(carboxylate)                                                                          of-Paris                                       ______________________________________                                         Length (mm)      15           15                                             Internal diameter (mm)                                                                          14           14                                             External Diameter (mm)                                                                          15.5         18                                             Weight of material (Kgm.sup.-2)                                                                 0.183        0.398                                          Length of gauze bandage (mm)                                                                    225          225                                            ______________________________________                                    

                  TABLE 2:                                                        ______________________________________                                                  Average Stress (N)                                                  Strain (%)  Poly(carboxylate)                                                                           Plaster-of-Paris                                    ______________________________________                                        5           16.3          21.1                                                10          22.4          26.4                                                12.5        24.2          28.8                                                ______________________________________                                    

These results show that the water-hardenable sheet materials of thepresent invention have excellent compressive strength combined with aconsiderable reduction in weight. Although the poly(carboxylate) cast ishalf the weight of the plaster-of-Paris cast, its compressive strengthis only slightly less. In addition, the poly(carboxylate) cast is notattacked by hot or cold water, is non-toxic and non-irritational, and istransparent to x-rays. The average time taken for a poly(carboxylate)cast to reach its maximum strength is about 8 hours, in comparison with24 hours for a plaster-of-Paris cast.

Further tensile stress tests carried out on samples of comparable sizeshow that a poly(carboxylate) cast is almost twice as strong as a castmade from plaster-of-Paris.

Examples 2-4 illustrate the preparation of suitable aluminosilicateglasses.

EXAMPLE 2

A series of glasses are prepared by fusing mixtures of silica, alumina,calcium and sodium carbonates as set out in Table 1 below in a platinumcrucible. After fusion the glass is poured off and cooled rapidly. Theglass compositions and fusion conditions are as follows:

                  Table 3                                                         ______________________________________                                                     I       II        III                                            ______________________________________                                        SiO.sub.2      118       143       118                                        Al.sub.2 O.sub.3                                                                             100       100       100                                        CaO*           110        32        55                                        Na.sub.2 O*    --         20       --                                         Fusion temperature (° C)                                                              1400      1500      1550                                       Time (hours)   21/4      33/4       1                                         ______________________________________                                         *added as carbonates to the fusion mixture.                              

The resultant glasses are dried and crushed until they pass through a350 mesh B.S. sieve.

EXAMPLE 3

The following compounds are mixed by milling and then heated in asillimanite crucible at 1250° C. until homogeneous (about 3 hours).

    ______________________________________                                        Silica                    143 gms.                                            Alumina                   100 gms.                                            Cryolite                   76 gms.                                            Fluorite                   56 gms.                                            Aluminium phosphate        73 gms.                                            ______________________________________                                    

The glass is prepared as described in Example 2 and crushed until itpasses through a 350 mesh B.S. sieve. The glass is found to have afluorine content of about 13.5% by weight (determined by the method ofA. C. D. Newman in `Analyst`, 1968 vol. 93 page 827).

EXAMPLE 4

A series of glasses are prepared by fusing mixtures of compounds inamounts and at fusion conditions as listed in Table 4:

                                      TABLE 4                                     __________________________________________________________________________              A    B    C    D    E    F    G    H    I                           __________________________________________________________________________    SiO.sub.2 180 gms                                                                             60 gms                                                                            120 gms                                                                            240 gms                                                                             87 gms                                                                            286 gms                                                                            120 gms                                                                            240 gms                                                                            120 gms                     Al.sub.2 O.sub.3                                                                        102 gms                                                                            102 gms                                                                            102 gms                                                                            102 gms                                                                            102 gms                                                                            200 gms                                                                            102 gms                                                                            102 gms                                                                            102 gms                     CaO*       56 gms                                                                            112 gms                                                                             93 gms                                                                            168 gms                                                                             78 gms                                                                             64 gms                                                                            168 gms                                                                            112 gms                                                                            101 gms                     Na.sub.2 O*                         39 gms                                    CaF.sub.2            26 gms                       156 gms                     Fusion temperature                                                                      1500-                                                                              1400-                                                                              1450 1450 1430 1400-                                                                              1525 1430-                                                                              1450                         (° C)                                                                           1550 1550                1500      1500                             Time      4 hrs                                                                              85 min                                                                             90 min                                                                             90 min                                                                             90 min                                                                             21/4 hrs                                                                           85 min                                                                             2 hrs                                                                              90 min                      __________________________________________________________________________     *added as carbonates to the fusion mixture                               

The resultant glasses are dried and crushed until they pass through a350 mesh B.S. sieve.

Examples 5 and 6 illustrate the preparation of acrylic copolymers.

EXAMPLE 5

This Example describes the preparation of a poly(carboxylate) cementusing as the cement-forming liquid an aqueous solution of a 1:4 moleratio copolymer of itaconic acid and acrylic acid. 2.5 parts by weightof ammonium persulphate and 200 parts by volume of water are placed in athree-necked round bottomed flask fitted with a condenser, and nitrogenis bubbled through the solution.

Solution A is 72.3 parts by weight of acrylic acid, 20 parts by volumeof propan-2-ol and 100 parts by volume of water. Solution B is 2.5 partsby weight of ammonium persulphate and 60 parts by volume of water. 32.7parts by weight of itaconic acid is divided into 24 equal parts. Thesolution in the flask is heated to boiling and additions of solutions Aand B and itaconic acid are made at approximately 5 minute intervals.After the completion of the additions the solution is heated for afurther two hours. The reaction product is concentrated to 50% w/wconcentration by vacuum distillation at 40°-45°.

There is produced an aqueous solution of an acrylic acid/itaconic acidcopolymer having a molecular weight of 18,000 and a viscosity of 26poise.

EXAMPLE 6

This Example describes the preparation of a poly(carboxylate) cementusing as the cement-forming liquid an aqueous solution of a 1:2 moleratio copolymer of itaconic acid and acrylic acid.

The procedure of Example 5 is repeated using 55.7 parts by weight ofacrylic acid and 49.8 parts by weight of itaconic acid. There isobtained a 50% w/w aqueous solution of an acrylic acid/itaconic acidcopolymer containing 47.4% itaconic acid units, having a molecularweight of 10,000 and a viscosity of 11 poise.

Examples 7 and 8 illustrate the use of the inert filler.

EXAMPLE 7

The following components are mixed by milling and then heated at 1100°C. for 11/2 hours.

    ______________________________________                                        SiO.sub.2              333 g                                                  Al.sub.2 O.sub.3       128 g                                                  CaF.sub.2              217 g                                                  Na.sub.3 AlF.sub.6     194 g                                                  AlPO.sub.4             136 g                                                  AlF.sub.3               31 g                                                  ______________________________________                                    

The resultant glass is cooled rapidly, dried, and crushed until itpasses through a 350 mesh B.S. sieve.

Mixtures of the glass powder are made up in various proportions withfine sand (Redhill AFS 80) of particle size from 100 to 200 B.S. meshand a liquid that is either a 47.3% w/w aqueous polyacrylic acidsolution or a 28% w/w aqueous ethylene-maleic acid (1:1) copolymersolution. All mixes are spatulated for 1 to 2 minutes and then placed ina hole 6.4 × 25.4 (diameter) mm in a wooden block. After levelling thecement mix the samples are aged for five days under ambient conditions.After ageing the condition of the cement is noted and the shrinkagemeasured by a depth gauge positioned at the centre of the cementsurface. The results are giving in Table 5 in which G represents glasspowder, P represents polyacrylic acid solution, E representsethylene-maleic acid copolymer solution and S represents sand.

                                      TABLE 5                                     __________________________________________________________________________    MIX PROPERTIES                                                                Composition                  SET CEMENT PROPERTIES                            Sample                                                                             (parts by               Shrinkage                                                                             State of                                 No.  weight) State of mix                                                                          Workability                                                                           (mm)    cement                                   __________________________________________________________________________    1    1G+1P   Very sticky,                                                                          Fairly  2.4     Fine cracks                                           thin mix.                                                                             difficult to                                                                  use.                                                     2    2G+1P   Extremely                                                                             Difficult to                                                                          0.8     Fine cracks                                           sticky. Stiff                                                                         use.                                                                  mix.                                                             3    3G+1P   Extremely                                                                             Very difficult                                                                        0.4     Very fine                                             sticky. Very                                                                          to use.         cracks                                                stiff.                                                           4    1G+1E   Very fluid.                                                                           Pourable                                                                              3.0     Split with                                            Not sticky.             huge cracks                              5    2G+1E   Fairly fluid                                                                          Fairly  1.6     Large cracks                                          Not sticky.                                                                           pourable                                                 6    3G+1E   Quite fluid.                                                                          Easy to use                                                                           0.4     Cracked                                               Not too sticky                                                   7    1G+1P+1S                                                                              Fluid mix.                                                                            Quite easy to                                                                         1.6     No cracks                                             Rather sticky.                                                                        use.                                                     8    2G+1P+2S                                                                              Doughy, quite                                                                         Very good to                                                                          0.6     No cracks                                             stiff. Not too                                                                        use.                                                                  sticky.                                                          9    1G+1P+2S                                                                              Fairly stiff.                                                                         Easy to use                                                                           1.2     No cracks                                             Not too sticky                                                   10   1G+1P+3S                                                                              Doughy, stiff                                                                         Very good to                                                                          0.6     No cracks                                             mix. Not very                                                                         use.                                                                  sticky.                                                          11   1G+1E+1S                                                                              Very fluid.                                                                           Pourable                                                                              1.8     Cracked                                               Not too                                                                       sticky.                                                          12   2G+1E+1S                                                                              Fluid mix.                                                                            Fairly easy to                                                                        0.6     No cracks                                                     use.                                                     13   3G+1E+3S                                                                              Doughy, Very good to                                                                          0.0     No cracks                                             stiff mix.                                                                            use.                                                     14   1G+1E+3S                                                                              Fairly fluid                                                                          Fairly easy to                                                                        0.8     No cracks                                                     use.                                                     15   2G+1E+3S                                                                              Doughy, very                                                                          Extremely easy                                                                        0.0     No cracks                                             stiff. Not                                                                            to use.                                                               sticky.                                                          __________________________________________________________________________

These results show that the addition of an inert filler decreases thestickiness of the mix and thus improves its workability, and decreasesshrinkage and the tendency for cracks to appear in the set cement.

EXAMPLE 8

The procedure of Example 7 is repeated replacing the sand with asbestostype M2(7-M) manufactured by Central Asbestos Co. Ltd. The result is asfollows:

    ______________________________________                                        Sam-             State                 State                                  ple  Composition of      Work- Shrinkage                                                                             of                                     No.  (by wt)     mix     ability                                                                             mm.     cement                                 ______________________________________                                        16   4G + 1A* + 1P                                                                             Fairly  Fair  0.5     No cracks                                               stiff                                                        ______________________________________                                         A represents asbestos type M2(7-M) ex Central Asbestos Co. Ltd.          

Examples 9-11 illustrate the use of a chelating agent.

EXAMPLE 9

This example describes the production of a poly(carboxylate) dentalcement from a fluoroaluminosilicate glass powder, and an aqueoussolution of poly(acrylic acid) containing tartaric acid as a chelatingagent.

The fluoroaluminosilicate glass powder is made by mixing together 175parts by weight of silica, 100 parts by weight of alumina, 30 parts byweight of cryolite, 207 parts by weight of calcium fluoride, 32 parts byweight of aluminium fluoride, and 60 parts by weight of aluminiumphosphate, and heating to a temperature of 1150° C. The glass is groundto a mesh size of 350 BSS mesh. The aqueous poly(acrylic acid) solutioncontains 50% by weight of a poly(acrylic acid) of average molecularweight 28,000 and 5% based on the weight of the poly(acrylic acid) oftartaric acid. The powder and the liquid are mixed together in the ratioof 3.5 gms. of powder to 1 milliliter of liquid. Hardness of the cementis measured by indentation 9 minutes after mixing. For comparison asample of the powder is mixed with an identical poly(acrylic acid)solution except that the tartaric acid is omitted, in a powder to liquidratio of 3 gms. of powder to 1 milliliter of liquid, giving a cement ofthe same consistency as the previous cement containing the chelatingagent. The results of setting time, working time, and hardness of thetwo cements are given below:

    ______________________________________                                        With Tartaric acid  Without tartaric acid                                     ______________________________________                                        Setting time (min)                                                                           31/4     6                                                     Working time (min)                                                                           2        21/2                                                  Wallace Indentation                                                           Number at 9 mins.                                                                            120      600                                                   ______________________________________                                    

EXAMPLE 10

This example describes the production of a poly(carboxylate) dentalcement using a fluoroaluminosilicate glass powder and an aqueoussolution of poly(acrylic acid) containing citric acid as a chelatingagent.

The procedure of Example 9 is repeated except that the tartaric acid isreplaced by 5% by weight of the poly(acrylic acid) of citric acid. Theresults of this cement are given below:

    ______________________________________                                        Setting time           33/4 mins                                              Working time           2 mins                                                 Wallace Indentation                                                           Number at 9 mins       347                                                    ______________________________________                                    

EXAMPLE 11

This example describes the production of a poly(carboxylate) dentalcement using a fluoroaluminosilicate glass powder and an aqueoussolution of poly(acrylic acid) containing tartaric acid as a chelatingagent and propan-2-ol as a stabilising agent.

The procedure of Example 9 is repeated except that the liquid containsin addition to the tartaric acid, 5%, based on the weight of thepoly(acrylic acid) of propan-2-ol. The results for this cement are givenbelow:

    ______________________________________                                        Setting time (min)     31/2                                                   Working time (min)     2                                                      Wallace Indentation                                                           Number 9 mins          120                                                    ______________________________________                                    

We claim:
 1. A water-hardenable sheet useful as a splinting material forportions of the human and animal anatomy which comprises a flexible webhaving adhered thereto a cement-forming material, said cement-formingmaterial comprising a water-soluble poly(carboxylic acid) or a precursorthereof that forms a poly(carboxylic acid) on contact with water and anion-leachable inorganic particulate material, which together form acement upon contact with water, said cement-forming material beingpresent in an amount sufficient to form a splinting material forportions of the human or animal anatomy upon the addition of the amountof water necessary to harden said sheet.
 2. A water-hardenable sheetaccording to claim 1 in which the flexible web has a porous structure.3. A water-hardenable sheet according to claim 1 in which the flexibleweb comprises a cellulosic fibrous material.
 4. A water-hardenable sheetaccording to claim 1 in which the poly(carboxylic acid) is a homopolymeror copolymer of acrylic acid.
 5. A water-hardenable sheet according toclaim 1 in which the precursor is a poly(carboxylic acid anhydride). 6.A water-hardenable sheet according to claim 1 in which thepoly(carboxylic acid) or precursor thereof has an average molecularweight of from 10,000 to 100,000.
 7. A water-hardenable sheet accordingto claim 1 in which the poly(carboxylic acid) or precursor thereof is inparticulate form, and has a degree of fineness such that it will passthrough a 150 B.S. mesh sieve.
 8. A water-hardenable sheet according toclaim 1 in which the ion-leachable inorganic particulate material is anoxide of a di- or poly-valent metal, or a salt of a weak acid and a di-or poly-valent metal.
 9. A water-hardenable sheet according to claim 8,in which the oxide is zinc oxide.
 10. A water-hardenable sheet accordingto claim 1 in which the ion-leachable inorganic particulate material isan aluminosilicate glass.
 11. A water-hardenable sheet according toclaim 10, in which the aluminosilicate glass has been prepared by fusinga mixture of alumina, silica, and calcium oxide together with up to 30%by weight, based on the total weight of the composition, of a fluoride,borate, phosphate, or carbonate flux.
 12. A water-hardenable sheetaccording to claim 10, in which the aluminosilicate glass is afluoroaluminosilicate glass.
 13. A water-hardenable sheet according toclaim 1 in which the ion-leachable inorganic particulate material has adegree of fineness such that it will pass through a 150 mesh B.S. sieve.14. A water-hardenable sheet according to claim 1 in which the weight ofthe cement-forming material is from 60 to 90% of the total weight of theflexible web and the cement-forming material.
 15. A water-hardenablesheet according to claim 14, in which the poly(carboxylic acid) orprecursor thereof and the ion-leachable inorganic particulate materialare present in the ratio of 1 to 100 parts by weight of ion-leachableinorganic particulate material to every 10 parts by weight of thepoly(carboxylic acid) or precursor thereof.
 16. A water-hardenable sheetaccording to claim 1 which further comprises a binder to assist theadherence of the ion-leachable inorganic particulate material to theflexible web.
 17. A water-hardenable sheet according to claim 16, inwhich the binder is polyvinyl alcohol, polyvinyl acetate, or partiallyhydrolysed polyvinyl acetate.
 18. A water-hardenable sheet according toclaim 16, in which the binder is present in an amount of from 0.1 to 1%by weight based on the combined weight of the acid and the inorganicmaterial.
 19. A water-hardenable sheet according to claim 1 whichfurther comprises an anti-shrinkage agent.
 20. A water-hardenable sheetaccording to claim 19 in which said anti-shrinkage agent is an inertparticulate filler.
 21. A water-hardenable sheet according to claim 1which further comprises a water soluble chelating agent.
 22. Awater-hardenable sheet according to claim 1 which further comprises awater insoluble polymer in particulate form.
 23. A water-hardenablesheet according to claim 22, in which the water insoluble polymer haspendant carboxylic acid groups.
 24. A water-hardenable sheet materialaccording to claim 22 in which the water insoluble polymer is acopolymer of an unsaturated aliphatic carboxylic acid and an unsaturatedaliphatic ester.
 25. A water-hardenable sheet according to claim 22 inwhich the water insoluble polymer is a copolymer of methacrylic acid andethyl acrylate.
 26. A water-hardenable sheet according to claim 10,wherein said aluminosilicate glass has been prepared by fusing a mixtureof 10 to 65% silica, 15 to 50% alumina, 0 to 50% calcium oxide and afluorine-containing fluxing agent to provide fluorine in an amount ofless than 14%, based on the weight of the composition.
 27. Awater-hardenable sheet according to claim 10, wherein the amount offluorine is less than 8%.
 28. A water-hardenable sheet according toclaim 27 wherein the aluminosilicate glass has a degree of fineness suchthat it will pass through a 150 mesh B.S. screen.
 29. A water-hardenablesheet according to claim 1 wherein said poly(carboxylic acid) is acopolymer of vinyl methyl ether and maleic anhydride.
 30. Awater-hardenable sheet according to claim 1 wherein the ion-leachableinorganic particulate material is a powder selected from the groupconsisting of an oxide of a di- or poly-valent metal, a salt of a weakacid and a di- or poly-valent metal and an aluminosilicate glass, andthe weight of the cement-forming material is from about 5 to 95% byweight of the flexible web and the cement-forming material.
 31. Awater-hardenable sheet according to claim 30 in which the ion-leachableinorganic particulate powder is a fluoroaluminosilicate glass.
 32. Awater-hardenable sheet according to claim 30 in which the weight of thecement-forming material is from 60 to 90% of the total weight of theflexible web and the cement-forming material.
 33. A water-hardenablesheet according to claim 32 in which the poly(carboxylic acid) orprecursor thereof and the ion-leachable inorganic particulate powder arepresent in the ratio of 1 to 100 parts by weight of ion-leachableinorganic particulate powder to every 10 parts by weight of thepoly(carboxylic acid) or precursor thereof.
 34. A water-hardenable sheetaccording to claim 30, in which the poly(carboxylic acid) is ahomopolymer or copolymer of acrylic acid.
 35. A water-hardenable sheetaccording to claim 34 in which the poly(carboxylic acid) has an averagemolecular weight of from 10,000 to 100,000.
 36. A substantially rigidsheet material comprising a flexible web and a poly(carboxylate) cementin layered relationship, the poly(carboxylate) cement having been formedby reaction in the presence of water of a water-soluble poly(carboxylicacid) or a precursor thereof that will be transformed into thepoly(carboxylic acid) on contact with water, and an ion-leachableinorganic particulate cement-forming material.
 37. A process for theproduction of a water-hardenable sheet material, which comprisesdepositing on to a flexible web reactants that react together in thepresence of water to form a poly(carboxylate) cement, said reactantsbeing a water soluble poly(carboxylic acid) or a precursor thereof thatwill be transformed into the poly(carboxylic acid) on contact with waterand an ion-leachable inorganic particulate cement-forming material.